1. Field
Performance monitoring of microelectronic components at a wafer level and a platform level.
2. Description of Related Art
Microelectronic components, such as transistors, resistors, diodes, capacitors, inductors, and various conductors and insulators, sometimes contain variations caused by the fabrication process. The variations in physical dimensions may produce device characteristics that deviate from the desired target. Such components may cause the die containing the components to have degraded performance or become totally unusable. To save cost, a chip manufacturer is interested in identifying a die that deviates from specified performance at a wafer level before the die is cut off from the wafer and packaged into an integrated chip (IC). Also, after a die is packaged into an IC, it is sometimes desirable to determine whether certain components in the IC satisfy specific requirements, e.g., for diagnostic or debugging purposes.
A wafer level test has been developed to evaluate analog characteristics of a group of dies on a wafer. Test circuits are built in the space between the dies on a wafer. Due to the limited space available, it is generally not possible to build a dedicated test circuit for each die. Thus, results obtained from the test circuits represent an average behavior of the die group instead of a single die. Such results cannot distinguish variations in the characteristics of each individual die within the die group. Moreover, these test circuits often require large dedicated pads to allow access by external measurement devices. Further, the test circuits cannot be reused after chip assembly because they become dissected after the dies are cut from the wafer.
Another approach has been developed to monitor the characteristics of a group of interconnected components within a die. Measurement devices have access to the component group but not the individual component. Thus, different component types with different characteristics (e.g., drain current, threshold voltage, effective channel length, channel width, sheet resistivity, and dielectric characteristics) are often combined into one measurement. Further, when measurements are taken from components connecting to an I/O buffer (which is a combination of multiple components), the results of the measurement are combined characteristics of multiple components including the buffer. Thus, analog characteristics of a single isolated component within a die are usually not available.